Ok I see. More than 24 tabs need to be opened on my screen to see this arrow, and even more if browser.tabs.tabMinWidth is set to 50 or less.Is there a trick to get this arrow visible much earlier, or always visible ?

Type about:support in the address bar - Enter - Open folderCreate chrome folder, create text file inside it and rename it to userChrome.cssOpen userChrome.css and paste the code aboveRestart the browser